# Wind Load Calculator

Pressure goes with velocity squared; height enters through the exposure power law.

- Page: https://jianzhujisuan.com/en/wind-load
- Category: Structural Design (https://jianzhujisuan.com/en/c/structural-design)
- Chinese version: https://jianzhujisuan.com/zh/wind-load.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Basic wind speed V 45 m/s, Exposure (ASCE 7) Exposure C - open terrain, Height above ground z 10 m, Topographic factor Kzt 1.0, Wind directionality Kd 0.85, Gust factor G 0.85, Shape coefficient Cp 0.8, Loaded area A 20 m²): **Design pressure 0.718 kPa**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Basic wind speed V | number | 45 | m/s |  |
| Exposure (ASCE 7) | select | Exposure C - open terrain | — |  |
| Height above ground z | number | 10 | m |  |
| Topographic factor Kzt | number | 1.0 | — |  |
| Wind directionality Kd | number | 0.85 | — |  |
| Gust factor G | number | 0.85 | — |  |
| Shape coefficient Cp | number | 0.8 | — |  |
| Loaded area A | number | 20 | m² |  |

## Formula

- **Height factor**: Kz = 2.01·(z/zg)^(2/α), z taken ≥ 15 ft
- **Velocity pressure**: qz = 0.613·Kz·Kzt·Kd·Ke·V² (N/m²)
- **Design pressure**: p = qz·G·Cp
- **Element force**: F = p·A
- **Basic velocity pressure**: qb = 0.5·ρ·V² (ρ = 1.25 kg/m³)
- **Ground elevation**: Ke = e^(−0.0000362·H), H in ft; taken as 1.0 here

## Worked example

45 m/s basic wind, exposure C, 10 m height, Kzt 1.0, Kd 0.85, G 0.85, Cp 0.8, 20 m² loaded: Kz 1.001, basic velocity pressure 1.266 kPa, qz 1.056 kPa, design pressure 0.718 kPa and 14.4 kN total force.

## Questions

### How do I calculate wind load?

Three steps. First turn the basic wind speed into a velocity pressure, qb = 0.5 rho V², using the return period your code requires. Second correct for height and terrain, Kz = 2.01 (z/zg)^(2/alpha). Third apply the gust factor and the shape coefficient for design pressure, p = qz G Cp, then multiply by the loaded area for force. At 45 m/s, 10 m, open terrain: 1.27 kPa basic, Kz about 1.0, 1.06 kPa velocity pressure and with G 0.85, 0.72 kPa on a windward face at Cp 0.8. For total push add windward 0.8 and leeward 0.5.

### Why is roof wind load negative?

Air accelerates over the ridge and pressure drops, so the roof feels an upward suction rather than a downward push. On pitches between 10 and 30 degrees the windward slope can reach Cp of −0.9 to −1.2, with higher local values at ridges and eaves. Purlins, roof sheets and self-drilling screws therefore have to be checked for uplift: a 20 m² sheet designed for 0.72 kPa downward may actually see 1.0 kPa upward. That reversal is why light steel roofs peel off in cyclones — the fixings were sized for pressure, not suction.

## Related tools

- [Snow Load Calculator](https://jianzhujisuan.com/en/snow-load): Steeper roofs hold less; above 60 degrees the shape coefficient is zero — but not at valleys and parapets.
- [Seismic Base Shear Calculator](https://jianzhujisuan.com/en/seismic-base-shear): Estimate the period, get the coefficient, multiply by seismic weight.
- [Bolt Capacity Calculator](https://jianzhujisuan.com/en/bolt-capacity): Shear or bearing, whichever is lower, governs — above 9 mm plate it is usually shear.
- [Punching Shear Calculator](https://jianzhujisuan.com/en/punching-shear): A column punching through a slab is a race between the perimeter ring and the load.

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